The present invention is related to wafer processing. More particularly, the present invention relates to an apparatus and method for processing wafers in multiple processing environments.
State of the art integrated circuits can contain up to 6 million transistors and more than 800 meters of wiring. There is a constant push to increase the number of transistors on wafer-based integrated circuits. As the number of transistors is increased there is a need to reduce the cross-talk between the closely packed wire in order to maintain high performance requirements. The semiconductor industry is continuously looking for new processes and new materials that can help to improve the performance of wafer-based integrated circuits. For example, there is considerable excitement within the industry surrounding the use and application of a group of materials generically referred to as low-k materials or low-dielectric materials. Low-k materials have been shown to reduce cross-talk and provide a transition into the fabrication of even smaller geometry integrated circuitry.
Low-k materials are required to be compatible with other wafer fabrication processes, they must exhibit good adhesion, high thermal stability and low film stress. The k value of a material depends on several factors including how the materials is deposited on the wafer. SiO2 has a k-value of approximately 4.0 and air has a k-value of 1.0. An ideal low-k material will have a k-value that approaches that of air. However, materials that exhibit k-values below 3.5 are considered low-k materials. Post treatment of coated materials can significantly reduce their observed k-value. For example, spin on glass materials and polymers can be treated to make porous siloxane coatings with k-values as low or below 2.0.
While low-k materials provide a promise for the fabrication of advanced micro circuitry, the deposition and subsequent treatment steps of low-k material in the wafer fabrication processing can lead to low throughput, increases in cost and low processing consistency. The wafer fabrication industry is continuously trying to balance state-of-the-art chip performance with the throughput, cost and consistency of wafer processing.
A wafer processing apparatus and method provides an apparatus and method for transferring a structure with a reaction surface from one processing environment to another processing environment. Preferably, the apparatus is configured to transfer a wafer from one processing environment to another processing environment. The wafer processing apparatus and method of the present invention transfers wafers with reaction surfaces from one processing environment to another processing environment while minimizing cross-contamination between processing environments and minimizing the depletion of processing chemicals during the transfer process. Further, the wafer processing apparatus and method transfers a reaction surface of a wafer into a chemical environment, while exposing the entire reaction surface to the processing environment quickly and with minimal initial convection during the transfers, thereby enhancing the consistency and uniformity of the wafer processing.
The apparatus of the instant invention has a first apparatus compartment configured to provide a first processing environment and a second apparatus compartment configured to provide a second processing environment. The first and the second apparatus compartments are coupled through a transfer passage that is capable of being opened and closed to create a transfer cavity and isolating a small transfer volume. The transfer volume is preferably less than five times the volume of the wafer, or wafers, being transferred and is most preferably less than twice the volume of the wafer, or wafers, being transferred in order to reduce the potential for cross-contamination between the first processing environment and the second processing environment during the transfer processes between the first and second apparatus compartments. According to an embodiment of the instant invention, the apparatus is provided with a vacuum source or a gas purge coupled to the transfer cavity for purging the transfer volume between transfers further reducing cross-contamination between the first processing environment and the second processing environment during the transfer process. The small transfer volume, utilized in the apparatus and method of the present invention, also reduces depletion of chemicals in a processing environment of the first and/or second apparatus compartment resulting from multiple transfers.
Preferably, the transfer cavity is formed from the transfer passage, a first movable table within the first apparatus compartment and a second movable table within the second apparatus compartment. The movable tables open and close ports of the transfer passage from within their respective compartments. The first and the second movable tables are configured to close together and isolate the wafer within the small transfer volume prior to exposing or transferring the wafer between the first processing environment and the second processing environment.
The apparatus preferably has a controllable chemical delivery system that maintains a chemical processing environment within the second compartment. Preferably, the chemical delivery system has a chemical sensor unit with one or more chemical sensors. The chemical sensor unit monitors the chemical composition, concentration or concentrations within the second apparatus compartment. The sensor unit controls a chemical supply, via feed back control circuitry, to deliver a processing chemical, or processing chemicals, to the second apparatus compartment in order to maintain a predetermined or selected composition or concentration value of the processing chemical in the second apparatus compartment.
According to an embodiment of the instant invention the chemical supply system is configured to deliver hydrated ammonia to the second apparatus compartment and the apparatus is configured for the treatment and aging of wafers coated with low-k spin-on-glass materials. At least one of the sensors is preferably a short path infrared sensor that measures the concentration of ammonia, water or both. If the measured concentration of ammonia or water is low, water or hydrated ammonia is supplied to the second apparatus compartment to reestablish the predetermined or selected concentration of hydrated ammonia within the second apparatus compartment. If the measured concentration of ammonia or water is high, the second apparatus compartment is purged with inert gas, or a vacuum is drawn on the second apparatus compartment, until the predetermined or selected concentration of hydrated ammonia is reestablished within the second apparatus compartment.
In operation, the wafer is placed on the first movable table within the first apparatus compartment with the second movable table in the closed position and capping the transfer passage between the first and second apparatus compartments. The processing environment within the first apparatus compartment is adjusted or maintained by any means known in the art to produce the desired outcome.
To expose and transfer the reaction surface of the wafer to the second processing environment, the second movable table is raised. Because the pressure and the chemical composition within the second processing environment is held substantially constant and because the entire reaction surface is exposed quickly to the chemical processing environment, the reaction surface of the wafer does not experience large fluctuations in chemical composition or exposure time to the surrounding processing environment. Thus, the method and apparatus of the present invention provides for consistent processing not only from wafer to wafer, but also throughout the surface of each wafer processed.
According to an alterative embodiment, prior to the step of exposing the wafer to the second processing environment, the transfer volume within the transfer cavity is purged to reduce contamination of the second processing environment with the small volume of the first processing environment captured within the transfer cavity.
According to a preferred embodiment of the invention, the second movable table is capable of being raised and lowered while the wafer is being exposed to the second processing environment. Moving the second movable table in an upward and downward motion creates a small amount of post exposure convection within the second processing environment and helps to quickly replenish processing chemicals at the reaction surface of the wafer and, thereby, helps to improve the throughput of the chemical processing step.
To transfer the wafer back to the first processing environment, the second movable table is placed in the closed position, thereby, capping the transfer passage and isolating the wafer in the transfer cavity. The first movable table is then lowered to expose and transfer the wafer back to the first processing environment. Alternatively, prior to the step of exposing and transferring the wafer back to the first processing environment, the transfer volume within the transfer cavity is purged to reduce contamination of the first processing environment with the small volume of the second processing environment captured within the transfer cavity. The purging includes steps such as drawing a vacuum on the transfer cavity and/or back filling the transfer cavity with a suitable processing environment or inert gas.
Preferably, the first movable table is configured to hold and support the wafer between transfers and support the wafer in the first apparatus compartment. Alternatively, the apparatus is configured with a wafer support for supporting the wafer above the first movable table, when the first movable table is in a lowered position. Within this embodiment, the wafer support comprises pin structures that pass through the first movable table, such that when the first movable table is lowered, the wafer is released onto the pins and when the first movable table is raised, the wafer is supported by the first movable table.
Preferably, the operation of the apparatus is automatically controlled by a controller or a computer, wherein a user selects a time of exposure of the wafer to the first and second processing environment, time of isolation of the wafer within the transfer cavity, concentrations of chemicals and the like. The at least one chemical sensor preferably continuously monitors the chemical composition or chemical concentration within the second process environment and is utilized to control the supply of the appropriate quantity of chemical or chemicals to maintain the selected composition or concentration.
The transfer mechanism of the instant invention is not limited to a two compartment wafer processing system. Any number of processing stations can be included within the apparatus, whereby wafers are moved from one station to the next and transferred between processing compartments by the mechanism described herein. Further, any number of more complex systems can be implemented to control the chemical environments within apparatus compartments. For example, each compartment can be equipped with an independently controllable chemical delivery system and monitoring system. Also, the transfer cavity itself can serve as a processing compartment and provide a separate and unique processing environment. According to the preferred embodiment of the invention, the apparatus is a modular processing station that is integrated into a multi-station wafer processing system.